The existing automobile seat which only has a headrest cannot support the face of a passenger from the side, and provides fixed limitation to the head to play a role of protecting the head when an accident occurs during driving of an automobile. However, if the side back cushion of the automobile is increased, time and labor are wasted in use when an external tool is required for mounting or dismounting. Sometimes, it is difficult to use if people just forget to carry the tool such as a screwdriver. Since such automobile side back cushion is integrally designed, the defect of wasting packaging materials will be caused.